Predicted Signs of One-Bond Spin−Spin Coupling Constants (1hJH-Y) across X−H−Y Hydrogen Bonds for Complexes with Y = 15N, 17O, and 19F

Abstract

Ab initio equation-of-motion coupled cluster (EOM-CCSD) calculations have been performed on a set of 44 complexes to obtain one-bond H−Y spin−spin coupling constants (1hJH-Y) across X−H−Y hydrogen bonds, with Y as the second-period elements 15N, 17O, and 19F. For complexes with traditional hydrogen bonds, the reduced Fermi-contact terms and the reduced one-bond spin−spin coupling constants (1hKH-Y) are negative. Since 1KX-H has been shown previously to be positive, a change of sign of these two coupling constants must occur along the proton-transfer coordinate. For complexes with symmetric X−H−X hydrogen bonds, the two reduced X−H coupling constants are equal and positive at equilibrium. For complexes stabilized by hydrogen bonds that have some proton-shared character, both 1hKH-Y and 1KX-H are also positive. The signs of all three reduced coupling constants (1hKH-Y, 2hKX-Y, and 1KX-H) that can arise between pairs of hydrogen-bonded atoms are interpreted in terms of the nuclear magnetic resonance triplet wave function model (NMRTWM). Determination of the signs of 1hKH-Y and 1KX-H could be useful for confirming the presence or absence of a proton-shared hydrogen bond.